Erectile dysfunction
Encyclopedia
Erectile dysfunction (ED) is sexual dysfunction characterized by the inability to develop or maintain an erection
of the penis
during sexual performance.
A penile erection is the hydraulic effect of blood
entering and being retained in sponge-like bodies within the penis. The process is often initiated as a result of sexual arousal
, when signals are transmitted from the brain
to nerves in the penis
. Erectile dysfunction is indicated when an erection is difficult to produce. There are various circulatory causes, including alteration of the voltage-gated potassium channel
, as in arsenic poisoning
from drinking water. The most important organic causes are cardiovascular disease and diabetes
, neurological problems (for example, trauma from prostatectomy
surgery), hormonal insufficiencies (hypogonadism
) and drug side effects
.
Psychological impotence is where erection or penetration fails due to thought
s or feeling
s (psychological reasons) rather than physical impossibility; this is somewhat less frequent but often can be helped. Notably in psychological impotence, there is a strong response to placebo treatment
. Erectile dysfunction, tied closely as it is about ideas of physical well being, can have severe psychological consequences.
Besides treating the underlying causes such as potassium deficiency or arsenic contamination of drinking water, the first line treatment of erectile dysfunction consists of a trial of PDE5 inhibitor
drugs (the first of which was sildenafil
or Viagra). In some cases, treatment can involve prostaglandin
tablets in the urethra
, injections into the penis, a penile prosthesis
, a penis pump or vascular reconstructive surgery.
The Latin term impotentia coeundi describes simple inability to insert the penis into the vagina
. It is now mostly replaced by more precise terms. The study of erectile dysfunction within medicine is covered by andrology
, a sub-field within urology
.
. There are several ways that erectile dysfunction is analyzed:
A few causes of impotence may be iatrogenic
(medically caused).
Surgical intervention for a number of different conditions may remove anatomical structures necessary to erection, damage nerves, or impair blood supply. Complete removal of the prostate gland or external beam radiotherapy of the gland are common causes of impotence; both are treatments for prostate cancer. Some studies have shown that male circumcision may result in an increased risk of impotence,
while others have found no such effect,
and another found the opposite.
A study in 2002 found that ED can also be associated with bicycling. The number of hours on a bike and/or the pressure on the penis from the saddle of an upright bicycle is directly related to erectile dysfunction.
A recent study suggests an epidemiological
association between chronic
periodontitis (periodontal
inflammation
) and erectile dysfunction, similarly to the association between periodontitis and coronary heart disease
s, and cerebrovascular disease
s. In all the three conditions (erectile dysfunction, coronary heart disease and cerebrovascular diseases), despite the epidemiological association with periodontitis, no causative connection has proved yet.
February 2011: Men who use non-steroidal anti-inflammatory drugs (NSAIDs) 3 times a day for more than 3 months are at a 22 percent increased risk of erectile dysfunction. A link between NSAID use and erectile dysfunction still existed for different age, race, ethnicity, smoker, diabetes, hypertension, high cholesterol, coronary diasease and others health problems. But due to benefit of NSAID, it's too early for men to avoid NSAIDs based solely on the research stated at Journal of Urology.
of the brain
. In both conditions, an intact neural system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system
leads to the secretion of nitric oxide
(NO), which causes the relaxation of smooth muscles of corpora cavernosa
(the main erectile tissue of penis), and subsequently penile erection. Additionally, adequate levels of testosterone
(produced by the testes) and an intact pituitary gland
are required for the development of a healthy erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply or psychological problems. Restriction of blood flow can arise from impaired endothelial function due to the usual causes associated with coronary artery disease, but can also be caused by prolonged exposure to bright light
.
s are generally done to exclude underlying disease, such as hypogonadism
and prolactinoma
. Diabetes is considered a disorder, but is also a risk. Impotence is also related to generally poor physical health, poor dietary habits, obesity
, and most specifically cardiovascular disease
such as coronary artery disease and peripheral vascular disease.
A useful and simple way to distinguish between physiological and psychological impotence is to determine whether the patient ever has an erection. If never, the problem is likely to be physiological; if sometimes (however rarely), it could be physiological or psychological. The current diagnostic and statistical manual of mental diseases (DSM-IV) has included a listing for impotence.
Duplex ultrasound:Duplex ultrasound
is used to evaluate blood flow, venous leak, signs of atherosclerosis, and scarring or calcification of erectile tissue. Injecting prostaglandin
, a hormone-like stimulator produced in the body, induces erection. Ultrasound is then used to see vascular dilation and measure penile blood pressure
.
Penile nerves function:Tests such as the bulbocavernosus reflex
test are used to determine if there is sufficient nerve sensation in the penis. The physician squeezes the glans (head) of the penis, which immediately causes the anus to contract if nerve function is normal. A physician measures the latency between squeeze and contraction by observing the anal sphincter or by feeling it with a gloved finger inserted past the anus.
Nocturnal penile tumescence (NPT):It is normal for a man to have five to six erections during sleep, especially during rapid eye movement (REM). Their absence may indicate a problem with nerve function or blood supply in the penis. There are two methods for measuring changes in penile rigidity and circumference during nocturnal erection: snap gauge and strain gauge. A significant proportion of men who have no sexual dysfunction nonetheless do not have regular nocturnal erections.
Penile biothesiometry:This test uses electromagnetic vibration to evaluate sensitivity and nerve function in the glans and shaft of the penis.
Dynamic infusion cavernosometry (DICC): technique in which fluid is pumped into the penis at a known rate and pressure. It gives a measurement of the vascular pressure in the corpus cavernosum during an erection.
Corpus cavernosometry:Cavernosography measurement of the vascular pressure in the corpus cavernosum. Saline is infused under pressure into the corpus cavernosum with a butterfly needle, and the flow rate needed to maintain an erection indicates the degree of venous leakage. The leaking veins responsible may be visualised by infusing a mixture of saline and x ray contrast medium and performing a cavernosogram.; Digital Subtraction Angiography: In DSA, the images are acquired digitally.
Magnetic resonance angiography (MRA): This is similar to magnetic resonance imaging
. Magnetic resonance angiography uses magnetic fields and radio waves to provide detailed images of the blood vessels. Doctors may inject a "contrast agent" into the patient's bloodstream that causes vascular tissues to stand out against other tissues. The contrast agent provides for enhanced information regarding blood supply and vascular anomalies.
Exercise, particularly aerobic exercise
is an effective treatment for erectile dysfunction.
When pharmacological methods fail, a purpose-designed external vacuum pump can be used to attain erection, with a separate compression ring fitted to the penis to maintain it. These pumps should be distinguished from other penis pumps (supplied without compression rings) which, rather than being used for temporary treatment of impotence, are claimed to increase penis length if used frequently, or vibrate as an aid to masturbation
. More drastically, inflatable or rigid penile implants may be fitted surgically. Medications carry risk of priapism
.
All these mechanical methods are based on simple principles of hydraulics and mechanics and are quite reliable, but have their disadvantages.
The cyclic nucleotide phosphodiesterase
s constitute a group of enzymes that catalyze the hydrolysis of the cyclic nucleotides cyclic AMP and cyclic GMP. They exist in different molecular forms and are unevenly distributed throughout the body.
One of the forms of phosphodiesterase is termed PDE5. The prescription PDE5 inhibitor
s sildenafil
(Viagra), vardenafil
(Levitra) and tadalafil
(Cialis) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP
to degrade.
Alprostadil
Alprostadil
in combination with the permeation enhancer DDAIP
has been approved in Canada under the brand name Vitaros as a topical cream first line treatment for erectile dysfunction.
Another treatment regimen is injection therapy. One of the following drugs is injected into the penis: papaverine
, phentolamine
, and prostaglandin E1
.
. Several types of FDA approved vacuum therapy devices are available with a doctor's prescription.
" or "natural" sexual enhancement products, but there are no clinical trials or scientific studies that support the effectiveness of these products for the treatment of erectile dysfunction, and synthetic chemical compounds similar to sildenafil have been found as adulterant
s in many of these products. The United States Food and Drug Administration has warned consumers that any sexual enhancement product that claims to work as well as prescription products is likely to contain such a contaminant.
initiated a boom in male impotence cures in the US in the 1920s and 1930s. His radio programs recommended expensive goat gland implants and "mercurochrome" injections as the path to restored male virility, including operations by surgeon Serge Voronoff
.
Modern drug therapy for ED made a significant advance in 1983, when British physiologist Giles Brindley
, Ph.D. dropped his trousers and demonstrated to a shocked Urodynamics Society audience his papaverine
-induced erection. The drug Brindley injected into his penis was a non-specific vasodilator, an alpha-blocking agent, and the mechanism of action was clearly corporal smooth muscle relaxation. The effect that Brindley discovered established the fundamentals for the later development of specific, safe, orally-effective drug therapies.
Gene therapy
is being developed that would allow for weeks or months long effect, supporting erections. This gene therapy involves injection of a transfer gene
, calcium-sensitive potassium channel (hMaxi-K), into the penis.
Tx2-6
A study done at the Medical College of Georgia
has found that venom from the Brazilian wandering spider
contains a toxin, called Tx2-6
, that causes erections. Scientists believe that combining this toxin with existing medication such as Viagra may lead to an effective treatment for erectile dysfunction.
Erection
Penile erection is a physiological phenomenon where the penis becomes enlarged and firm. Penile erection is the result of a complex interaction of psychological, neural, vascular and endocrine factors, and is usually, though not exclusively, associated with sexual arousal...
of the penis
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
during sexual performance.
A penile erection is the hydraulic effect of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
entering and being retained in sponge-like bodies within the penis. The process is often initiated as a result of sexual arousal
Sexual arousal
Sexual arousal, or sexual excitement, is the arousal of sexual desire, during or in anticipation of sexual activity. Things that precipitate human sexual arousal are called erotic stimuli, or colloquially known as turn-ons. There are many potential stimuli, both physical or mental, which can cause...
, when signals are transmitted from the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
to nerves in the penis
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
. Erectile dysfunction is indicated when an erection is difficult to produce. There are various circulatory causes, including alteration of the voltage-gated potassium channel
Voltage-gated potassium channel
Voltage-gated potassium channels are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. During action potentials, they play a crucial role in returning the depolarized cell to a resting state....
, as in arsenic poisoning
Arsenic poisoning
Arsenic poisoning is a medical condition caused by increased levels of the element arsenic in the body. Arsenic interferes with cellular longevity by allosteric inhibition of an essential metabolic enzyme...
from drinking water. The most important organic causes are cardiovascular disease and diabetes
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
, neurological problems (for example, trauma from prostatectomy
Prostatectomy
A prostatectomy is the surgical removal of all or part of the prostate gland. Abnormalities of the prostate, such as a tumour, or if the gland itself becomes enlarged for any reason, can restrict the normal flow of urine along the urethra....
surgery), hormonal insufficiencies (hypogonadism
Hypogonadism
Hypogonadism is a medical term for decreased functional activity of the gonads. Low testosterone is caused by a decline or deficiency in gonadal production of testosterone in males...
) and drug side effects
Adverse drug reaction
An adverse drug reaction is an expression that describes harm associated with the use of given medications at a normal dosage. ADRs may occur following a single dose or prolonged administration of a drug or result from the combination of two or more drugs...
.
Psychological impotence is where erection or penetration fails due to thought
Thought
"Thought" generally refers to any mental or intellectual activity involving an individual's subjective consciousness. It can refer either to the act of thinking or the resulting ideas or arrangements of ideas. Similar concepts include cognition, sentience, consciousness, and imagination...
s or feeling
Feeling
Feeling is the nominalization of the verb to feel. The word was first used in the English language to describe the physical sensation of touch through either experience or perception. The word is also used to describe experiences, other than the physical sensation of touch, such as "a feeling of...
s (psychological reasons) rather than physical impossibility; this is somewhat less frequent but often can be helped. Notably in psychological impotence, there is a strong response to placebo treatment
Placebo effect
Placebo effect may refer to:* Placebo effect, the tendency of any medication or treatment, even an inert or ineffective one, to exhibit results simply because the recipient believes that it will work...
. Erectile dysfunction, tied closely as it is about ideas of physical well being, can have severe psychological consequences.
Besides treating the underlying causes such as potassium deficiency or arsenic contamination of drinking water, the first line treatment of erectile dysfunction consists of a trial of PDE5 inhibitor
PDE5 inhibitor
A phosphodiesterase type 5 inhibitor, often shortened to PDE5 inhibitor, is a drug used to block the degradative action of phosphodiesterase type 5 on cyclic GMP in the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis...
drugs (the first of which was sildenafil
Sildenafil
Sildenafil citrate, sold as Viagra, Revatio and under various other trade names, is a drug used to treat erectile dysfunction and pulmonary arterial hypertension . It was originally developed by British scientists and then brought to market by the US-based pharmaceutical company Pfizer...
or Viagra). In some cases, treatment can involve prostaglandin
Prostaglandin
A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....
tablets in the urethra
Urethra
In anatomy, the urethra is a tube that connects the urinary bladder to the genitals for the removal of fluids out of the body. In males, the urethra travels through the penis, and carries semen as well as urine...
, injections into the penis, a penile prosthesis
Penile prosthesis
A penile prosthesis is a medical device implanted in the penis requiring a surgical procedure. The device is often used for men with organic or treatment-resistant psychogenic impotence who suffer from erectile dysfunction...
, a penis pump or vascular reconstructive surgery.
The Latin term impotentia coeundi describes simple inability to insert the penis into the vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
. It is now mostly replaced by more precise terms. The study of erectile dysfunction within medicine is covered by andrology
Andrology
Andrology is the medical specialty that deals with male health, particularly relating to the problems of the male reproductive system and urological problems that are unique to men. It is the counterpart to gynaecology, which deals with medical issues which are specific to the female reproductive...
, a sub-field within urology
Urology
Urology is the medical and surgical specialty that focuses on the urinary tracts of males and females, and on the reproductive system of males. Medical professionals specializing in the field of urology are called urologists and are trained to diagnose, treat, and manage patients with urological...
.
Signs and symptoms
Erectile dysfunction is characterized by the regular or repeated inability to obtain or maintain an erectionErection
Penile erection is a physiological phenomenon where the penis becomes enlarged and firm. Penile erection is the result of a complex interaction of psychological, neural, vascular and endocrine factors, and is usually, though not exclusively, associated with sexual arousal...
. There are several ways that erectile dysfunction is analyzed:
- Obtaining full erections at some times, such as when asleep (when the mind and psychological issues, if any, are less present), tends to suggest the physical structures are functionally working.
- Other factors leading to erectile dysfunction are diabetes mellitusDiabetes mellitusDiabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
(causing neuropathy).
Causes
- Drugs (anti-depressants (SSRIs) and nicotineNicotineNicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
are most common) - Neurogenic disorders (spinal cordSpinal cord injuryA spinal cord injury refers to any injury to the spinal cord that is caused by trauma instead of disease. Depending on where the spinal cord and nerve roots are damaged, the symptoms can vary widely, from pain to paralysis to incontinence...
and brain injuriesTraumatic brain injuryTraumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...
, nerve disorders such as Parkinson's diseaseParkinson's diseaseParkinson's disease is a degenerative disorder of the central nervous system...
, Alzheimer's diseaseAlzheimer's diseaseAlzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
, multiple sclerosisMultiple sclerosisMultiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
, and strokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
) - Cavernosal disorders (Peyronie's diseasePeyronie's diseasePeyronie's Disease Peyronie's Disease Peyronie's Disease (also known as "Induratio penis plastica", or more recently Chronic Inflammation of the Tunica Albuginea (CITA), is a connective tissue disorder involving the growth of fibrous plaques in the soft tissue of the penis affecting up to 10% of men...
) - Psychological causes: performance anxiety, stressStress (biology)Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
, mental disorders (clinical depressionClinical depressionMajor depressive disorder is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and by loss of interest or pleasure in normally enjoyable activities...
, schizophreniaSchizophreniaSchizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
, substance abuseSubstance abuseA substance-related disorder is an umbrella term used to describe several different conditions associated with several different substances .A substance related disorder is a condition in which an individual uses or abuses a...
, panic disorderPanic disorderPanic disorder is an anxiety disorder characterized by recurring severe panic attacks. It may also include significant behavioral change lasting at least a month and of ongoing worry about the implications or concern about having other attacks. The latter are called anticipatory attacks...
, generalized anxiety disorder, personality disorderPersonality disorderPersonality disorders, formerly referred to as character disorders, are a class of personality types and behaviors. Personality disorders are noted on Axis II of the Diagnostic and Statistical Manual of Mental Disorders or DSM-IV-TR of the American Psychiatric Association.Personality disorders are...
s or traits), psychological problems, negative feelings. - Surgery (radiation therapyRadiation therapyRadiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
, surgery of the colonColon (anatomy)The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
, prostate, bladderBladderBladder usually refers to an anatomical hollow organBladder may also refer to:-Biology:* Urinary bladder in humans** Urinary bladder ** Bladder control; see Urinary incontinence** Artificial urinary bladder, in humans...
, or rectum may damage the nerves and blood vessels involved in erection. Prostate and bladder cancerBladder cancerBladder cancer is any of several types of malignant growths of the urinary bladder. It is a disease in which abnormal cells multiply without control in the bladder. The bladder is a hollow, muscular organ that stores urine; it is located in the pelvis...
surgery often require removing tissue and nerves surrounding a tumor, which increases the risk for impotence) - AgeingAgeingAgeing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...
. It is four times higher in men in their 60s than in men in their 40s. - Kidney failure
- Diseases such as diabetes and multiple sclerosis (MS). While these two causes have not been proven they’re likely suspects as they cause issues with both the blood flow and nervous systems.
- Lifestyle: smoking is a key cause of erectile dysfunction. Smoking causes impotence because it promotes arterial narrowingAtherosclerosisAtherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
. See also Tobacco and health.
A few causes of impotence may be iatrogenic
Iatrogenesis
Iatrogenesis, or an iatrogenic artifact is an inadvertent adverse effect or complication resulting from medical treatment or advice, including that of psychologists, therapists, pharmacists, nurses, physicians and dentists...
(medically caused).
Surgical intervention for a number of different conditions may remove anatomical structures necessary to erection, damage nerves, or impair blood supply. Complete removal of the prostate gland or external beam radiotherapy of the gland are common causes of impotence; both are treatments for prostate cancer. Some studies have shown that male circumcision may result in an increased risk of impotence,
while others have found no such effect,
and another found the opposite.
A study in 2002 found that ED can also be associated with bicycling. The number of hours on a bike and/or the pressure on the penis from the saddle of an upright bicycle is directly related to erectile dysfunction.
A recent study suggests an epidemiological
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
association between chronic
Chronic
Chronic may refer to:* Chronic , a disease that is long-lasting and reoccurring.* Chronic toxicity, a substance with toxic effects after continuous or repeated exposure* The Chronic, a 1992 album by Dr. Dre...
periodontitis (periodontal
Gingiva
The gingiva , or gums, consists of the mucosal tissue that lies over the mandible and maxilla inside the mouth.-General description:...
inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
) and erectile dysfunction, similarly to the association between periodontitis and coronary heart disease
Coronary heart disease
Coronary artery disease is the end result of the accumulation of atheromatous plaques within the walls of the coronary arteries that supply the myocardium with oxygen and nutrients. It is sometimes also called coronary heart disease...
s, and cerebrovascular disease
Cerebrovascular disease
Cerebrovascular disease is a group of brain dysfunctions related to disease of the blood vessels supplying the brain. Hypertension is the most important cause; it damages the blood vessel lining, endothelium, exposing the underlying collagen where platelets aggregate to initiate a repairing process...
s. In all the three conditions (erectile dysfunction, coronary heart disease and cerebrovascular diseases), despite the epidemiological association with periodontitis, no causative connection has proved yet.
February 2011: Men who use non-steroidal anti-inflammatory drugs (NSAIDs) 3 times a day for more than 3 months are at a 22 percent increased risk of erectile dysfunction. A link between NSAID use and erectile dysfunction still existed for different age, race, ethnicity, smoker, diabetes, hypertension, high cholesterol, coronary diasease and others health problems. But due to benefit of NSAID, it's too early for men to avoid NSAIDs based solely on the research stated at Journal of Urology.
Pathophysiology
Penile erection is managed by two different mechanisms. The first one is the reflex erection, which is achieved by directly touching the penile shaft. The second is the psychogenic erection, which is achieved by erotic or emotional stimuli. The former uses the peripheral nerves and the lower parts of the spinal cord, whereas the latter uses the limbic systemLimbic system
The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
of the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
. In both conditions, an intact neural system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
leads to the secretion of nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
(NO), which causes the relaxation of smooth muscles of corpora cavernosa
Corpus cavernosum penis
The corpus cavernosum penis is one of a pair of sponge-like regions of erectile tissue which contain most of the blood in the penis during penile erection...
(the main erectile tissue of penis), and subsequently penile erection. Additionally, adequate levels of testosterone
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...
(produced by the testes) and an intact pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
are required for the development of a healthy erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply or psychological problems. Restriction of blood flow can arise from impaired endothelial function due to the usual causes associated with coronary artery disease, but can also be caused by prolonged exposure to bright light
Over-illumination
Over-illumination is the presence of lighting intensity beyond that required for a specified activity. Over-illumination was commonly ignored between 1950 and 1995, especially in office and retail environments; only since then has the interior design community begun to reconsider this practice.The...
.
Diagnosis
There are no formal tests to diagnose erectile dysfunction. Some blood testBlood test
A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick....
s are generally done to exclude underlying disease, such as hypogonadism
Hypogonadism
Hypogonadism is a medical term for decreased functional activity of the gonads. Low testosterone is caused by a decline or deficiency in gonadal production of testosterone in males...
and prolactinoma
Prolactinoma
A prolactinoma is a benign tumor of the pituitary gland that produces a hormone called prolactin. It is the most common type of pituitary tumor...
. Diabetes is considered a disorder, but is also a risk. Impotence is also related to generally poor physical health, poor dietary habits, obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
, and most specifically cardiovascular disease
Cardiovascular disease
Heart disease or cardiovascular disease are the class of diseases that involve the heart or blood vessels . While the term technically refers to any disease that affects the cardiovascular system , it is usually used to refer to those related to atherosclerosis...
such as coronary artery disease and peripheral vascular disease.
A useful and simple way to distinguish between physiological and psychological impotence is to determine whether the patient ever has an erection. If never, the problem is likely to be physiological; if sometimes (however rarely), it could be physiological or psychological. The current diagnostic and statistical manual of mental diseases (DSM-IV) has included a listing for impotence.
Duplex ultrasound:Duplex ultrasound
Duplex ultrasound
Duplex ultrasonography is a form of medical ultrasonography that incorporates two elements:...
is used to evaluate blood flow, venous leak, signs of atherosclerosis, and scarring or calcification of erectile tissue. Injecting prostaglandin
Prostaglandin
A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....
, a hormone-like stimulator produced in the body, induces erection. Ultrasound is then used to see vascular dilation and measure penile blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
.
Penile nerves function:Tests such as the bulbocavernosus reflex
Bulbocavernosus reflex
The bulbocavernosus reflex is a polysynaptic reflex that is useful in testing for spinal shock and gaining information about the state of spinal cord injuries . The test involves monitoring anal sphincter contraction in response to squeezing the glans penis or tugging on an indwelling Foley...
test are used to determine if there is sufficient nerve sensation in the penis. The physician squeezes the glans (head) of the penis, which immediately causes the anus to contract if nerve function is normal. A physician measures the latency between squeeze and contraction by observing the anal sphincter or by feeling it with a gloved finger inserted past the anus.
Nocturnal penile tumescence (NPT):It is normal for a man to have five to six erections during sleep, especially during rapid eye movement (REM). Their absence may indicate a problem with nerve function or blood supply in the penis. There are two methods for measuring changes in penile rigidity and circumference during nocturnal erection: snap gauge and strain gauge. A significant proportion of men who have no sexual dysfunction nonetheless do not have regular nocturnal erections.
Penile biothesiometry:This test uses electromagnetic vibration to evaluate sensitivity and nerve function in the glans and shaft of the penis.
Dynamic infusion cavernosometry (DICC): technique in which fluid is pumped into the penis at a known rate and pressure. It gives a measurement of the vascular pressure in the corpus cavernosum during an erection.
Corpus cavernosometry:Cavernosography measurement of the vascular pressure in the corpus cavernosum. Saline is infused under pressure into the corpus cavernosum with a butterfly needle, and the flow rate needed to maintain an erection indicates the degree of venous leakage. The leaking veins responsible may be visualised by infusing a mixture of saline and x ray contrast medium and performing a cavernosogram.; Digital Subtraction Angiography: In DSA, the images are acquired digitally.
Magnetic resonance angiography (MRA): This is similar to magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
. Magnetic resonance angiography uses magnetic fields and radio waves to provide detailed images of the blood vessels. Doctors may inject a "contrast agent" into the patient's bloodstream that causes vascular tissues to stand out against other tissues. The contrast agent provides for enhanced information regarding blood supply and vascular anomalies.
Treatment
Treatment depends on the cause.Exercise, particularly aerobic exercise
Aerobic exercise
Aerobic exercise is physical exercise of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism...
is an effective treatment for erectile dysfunction.
When pharmacological methods fail, a purpose-designed external vacuum pump can be used to attain erection, with a separate compression ring fitted to the penis to maintain it. These pumps should be distinguished from other penis pumps (supplied without compression rings) which, rather than being used for temporary treatment of impotence, are claimed to increase penis length if used frequently, or vibrate as an aid to masturbation
Masturbation
Masturbation refers to sexual stimulation of a person's own genitals, usually to the point of orgasm. The stimulation can be performed manually, by use of objects or tools, or by some combination of these methods. Masturbation is a common form of autoeroticism...
. More drastically, inflatable or rigid penile implants may be fitted surgically. Medications carry risk of priapism
Priapism
Priapism is a potentially harmful and painful medical condition in which the erect penis or clitoris does not return to its flaccid state, despite the absence of both physical and psychological stimulation, within four hours. There are two types of priapism: low-flow and high-flow. Low-flow...
.
All these mechanical methods are based on simple principles of hydraulics and mechanics and are quite reliable, but have their disadvantages.
Medication
Phosphodiesterase type 5 inhibitorsThe cyclic nucleotide phosphodiesterase
Phosphodiesterase
A phosphodiesterase is any enzyme that breaks a phosphodiester bond. Usually, people speaking of phosphodiesterase are referring to cyclic nucleotide phosphodiesterases, which have great clinical significance and are described below...
s constitute a group of enzymes that catalyze the hydrolysis of the cyclic nucleotides cyclic AMP and cyclic GMP. They exist in different molecular forms and are unevenly distributed throughout the body.
One of the forms of phosphodiesterase is termed PDE5. The prescription PDE5 inhibitor
PDE5 inhibitor
A phosphodiesterase type 5 inhibitor, often shortened to PDE5 inhibitor, is a drug used to block the degradative action of phosphodiesterase type 5 on cyclic GMP in the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis...
s sildenafil
Sildenafil
Sildenafil citrate, sold as Viagra, Revatio and under various other trade names, is a drug used to treat erectile dysfunction and pulmonary arterial hypertension . It was originally developed by British scientists and then brought to market by the US-based pharmaceutical company Pfizer...
(Viagra), vardenafil
Vardenafil
Vardenafil is a PDE5 inhibitor used for treating erectile dysfunction that is sold under the trade names Levitra and Staxyn.-History:...
(Levitra) and tadalafil
Tadalafil
Tadalafil is a PDE5 inhibitor, currently marketed in pill form for treating erectile dysfunction under the name Cialis; and under the name Adcirca for the treatment of pulmonary arterial hypertension...
(Cialis) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP
Cyclic guanosine monophosphate
Cyclic guanosine monophosphate is a cyclic nucleotide derived from guanosine triphosphate . cGMP acts as a second messenger much like cyclic AMP...
to degrade.
Alprostadil
Alprostadil
Alprostadil
Prostaglandin E1 , known pharmaceutically as alprostadil, is a prostaglandin. It is a drug used in the treatment of erectile dysfunction and has vasodilatory properties.-Sexual dysfunction:...
in combination with the permeation enhancer DDAIP
DDAIP
DDAIP is a pharmaceutical ingredient added to topical products to increase penetration through the skin. Chemically, DDAIP is an ester of N,N-dimethylalanine and dodecanol. DDAIP is typically formulated as its hydrochloride salt...
has been approved in Canada under the brand name Vitaros as a topical cream first line treatment for erectile dysfunction.
Another treatment regimen is injection therapy. One of the following drugs is injected into the penis: papaverine
Papaverine
Papaverine is an opium alkaloid antispasmodic drug, used primarily in the treatment of visceral spasm, vasospasm , and occasionally in the treatment of erectile dysfunction...
, phentolamine
Phentolamine
Phentolamine is a reversible nonselective alpha-adrenergic antagonist. -Mechanism:Its primary action is vasodilation due to α1 blockade....
, and prostaglandin E1
Prostaglandin E1
Prostaglandin E1 , known pharmaceutically as alprostadil, is a prostaglandin. It is a drug used in the treatment of erectile dysfunction and has vasodilatory properties.-Sexual dysfunction:...
.
Surgery
Often, as a last resort if other treatments have failed, the most common procedure is prosthetic implants which involves the insertion of artificial rods into the penis.Devices
The device helps draw blood into the penis by applying negative pressure. This type of device is sometimes referred to as penis pump and may be used just prior to sexual intercourseSexual intercourse
Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...
. Several types of FDA approved vacuum therapy devices are available with a doctor's prescription.
Alternative medicine
The FDA does not recommend alternative therapies to treat sexual function. There are many different products advertised as "herbal viagraHerbal viagra
Herbal viagra is a name that can be given to any herbal product advertised as treating erectile dysfunction. The name "herbal viagra" is taken from the brand name Viagra, under which drug company Pfizer sells sildenafil citrate, a drug that is used to treat erectile dysfunction...
" or "natural" sexual enhancement products, but there are no clinical trials or scientific studies that support the effectiveness of these products for the treatment of erectile dysfunction, and synthetic chemical compounds similar to sildenafil have been found as adulterant
Adulterant
An adulterant is a chemical substance which should not be contained within other substances for legal or other reasons. Adulterants may be intentionally added to more expensive substances to increase visible quantities and reduce manufacturing costs or for some other deceptive or malicious purpose...
s in many of these products. The United States Food and Drug Administration has warned consumers that any sexual enhancement product that claims to work as well as prescription products is likely to contain such a contaminant.
History
Dr. John R. BrinkleyJohn R. Brinkley
John Romulus Brinkley was a controversial American medical doctor who experimented with xenotransplantation of goat glands into humans as a means of curing male impotence in clinics across several states, and an advertising and radio pioneer who began the era of Mexican border blaster radio...
initiated a boom in male impotence cures in the US in the 1920s and 1930s. His radio programs recommended expensive goat gland implants and "mercurochrome" injections as the path to restored male virility, including operations by surgeon Serge Voronoff
Serge Voronoff
Serge Abrahamovitch Voronoff was a French surgeon of Russian extraction who gained fame for his technique of grafting monkey testicle tissue on to the testicles of men for purportedly therapeutic purposes while working in France in the 1920s and 1930s. The technique brought him a great deal of...
.
Modern drug therapy for ED made a significant advance in 1983, when British physiologist Giles Brindley
Giles Brindley
Sir Giles Skey Brindley, GBE , is a British physiologist, musicologist and composer.He made important contributions to the treatment of erectile dysfunction, and is perhaps best known for an unusual scientific presentation at the 1983 Las Vegas meeting of the American Urological Association, where...
, Ph.D. dropped his trousers and demonstrated to a shocked Urodynamics Society audience his papaverine
Papaverine
Papaverine is an opium alkaloid antispasmodic drug, used primarily in the treatment of visceral spasm, vasospasm , and occasionally in the treatment of erectile dysfunction...
-induced erection. The drug Brindley injected into his penis was a non-specific vasodilator, an alpha-blocking agent, and the mechanism of action was clearly corporal smooth muscle relaxation. The effect that Brindley discovered established the fundamentals for the later development of specific, safe, orally-effective drug therapies.
Research
Gene therapyGene therapy
Gene therapy
Gene therapy is the insertion, alteration, or removal of genes within an individual's cells and biological tissues to treat disease. It is a technique for correcting defective genes that are responsible for disease development...
is being developed that would allow for weeks or months long effect, supporting erections. This gene therapy involves injection of a transfer gene
Transfer gene
Transfer operon, commonly called tra operon, or tra genes, are some of the genes necessary for non-sexual transfer of genetic material in both gram-positive and gram-negative bacteria...
, calcium-sensitive potassium channel (hMaxi-K), into the penis.
Tx2-6
A study done at the Medical College of Georgia
Medical College of Georgia
Georgia Health Sciences University formerly known as, and now home of the, Medical College of Georgia , is a public academic health center, with its main campus located in the Medical District of Augusta, Georgia. It is the smallest of four research universities in the University System of Georgia...
has found that venom from the Brazilian wandering spider
Brazilian wandering spider
Phoneutria, commonly known as Brazilian wandering spiders, armed spiders , or banana spiders , are a genus of aggressive and highly venomous spiders found in tropical South and Central America...
contains a toxin, called Tx2-6
Tx2-6
Tx2-6 is a toxin found in the venom of the Brazilian wandering spider, Phoneutria nigriventer . It is a peptide of 48 residues, molecular weight 5291.3. This peptide is cleaved from a longer precursor with a signal peptide and a glutamine-rich propeptide. It can cause priapism...
, that causes erections. Scientists believe that combining this toxin with existing medication such as Viagra may lead to an effective treatment for erectile dysfunction.